Voltage regulation system for vacuum tube amplifiers



June 18, 1940. Y NE 2,204,571

VOLTAGE REGULATION SYSTEM FOR VACUUM TUBE AMPLIFIERS Filed April 21, 1938 lg v l 2a 2 E, gys 5% E0 ,2

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IN V EN TOR.

John FByvne Win55? Patented June 18, 1940 PATENT orrlcs VOLTAGE REGULATION SYSTEM FOR VACUUM TUBE AMPLIFIERS John F. Byi'ne, Cedar Rapids, Iowa, assignor to Collins Radio Company, Cedar Rapids, Iowa, a

corporation of Iowa ApplicationApril 21, 1938, Serial No. 203,435 7 Claims. (01. 179 -171) .Mly invention relates broadly to electron tube amplification circuitsand more particularly to a voltage regulation system therefor.

One of the. objects of my invention is .to provide an electron tube amplification circuit having voltage regulating means for maintaining substantially constant output voltage independently of load conditions.

Another object of my invention to provide to voltage regulating means controlled jointly from the input and the output circuits of an electron tube amplifier and operative to maintain substantially constant output voltage under load and open circuit conditions.

Still another object of my invention is to provide normally balanced circuit means in'cthe input circuit of an electrontube amplifiehoperative to deliver a differential of voltage in the in put circuit upon connection ofa load in the out- 20 put circuit of the amplifier to counteract for voltage variations in the output circuit due to theload current.

A further object of my inventionis to provide a regulating transformer connected in the input .25 circuit of an electron tube amplifier for voltage constant voltage conditions in the output circuit. l l i Other and further objects of my invention reside in the system and circuit arrangements hereinafter more fully described with reference to the accompanying drawing, in which? Figure 1 is, a schematic diagram illustrating the essential factors in the voltage regulating systemfor electron tube amplifiers of my invention; and Fig. 2 is a schematic diagramof a modified form of electron-tube amplifier embodying the voltage regulation system of my invention.

My invention deals with a system of voltage regulation, as applied to a vacuum tube amplifier which operates into a load of variable impedance characteristic, This type of amplifier operation is encountered when theamplifier is 5 followed in cascade by an amplifier of the Class B type, which requires driving power not proportional to the square of the input voltage.

The system as illustrated in Fig. 1 in schematic form includes an electron tube 1 provided with anode la, grid lg, and cathode Ic. An output 5 transformer 2 comprises conventional primary. and secondary windings 2a and 2b, respectively, and an auxiliarywinding 2c in the nature of a secondary of an auto-transformer arrangement employing the same primary winding 2a as the conventional arrangement. The input source of energy is schematically indicated at 3, and the regulating transformer is shown at 4, with pri-v mary 4a and secondary 4b wound on a magnetic core. Suitable sources of bias potential and power are represented by batteries at 6 in.

. winding and a blocking condenser 5 which prevents the flow of direct current from the sources 6 and 1. The alternating potentials E1 and Em,"Of the input source 3 and the secondary 20 respectively, are connected in phase opposition under no load conditions in the output circuit, so that the magnetic fields in the regulating transformer 4 are balanced.- The effective grid Voltage is designated Eg, and the output 7 Voltage E0. In operation, this output voltage E0 is not materially affected by load demands, due to the functioning of the voltage regulating system of my invention.

With thegrid voltage applied, the amplified voltage E0 appears in the output circuit, and simultaneously the voltage Em is induced in the l auxiliary winding 20 of the output transformer 2. The value of this voltage is such that it is equal to and substantially in phase opposition with the grid voltage E1 when no load is in the output circuit. Under these conditions, the voltage appearing across. the primary 4a of the magnetic core regulating transformer 4 is zero. When a load is connected in. the output circuit, theoutput voltage E0 tends to decrease; at the same time, the monitoring voltage Em tends to decrease, and in so doing, the difference between the grid voltage E1 and the monitoring voltage Em appears across the transformer 4. This ings.

' put source 3".

transformer is so phased that the grid voltage Eg is increased, and the decrease in output voltage due to load is greatly reduced. The amount of stabilization of the output voltage will depend upon the turns ratio of the regulating transformer t, the greater the turns ratio, the greater the stabilization.

Fig. 2 shows schematically a modified form of my invention operativein the same manner as that illustrated in Fig. 1. In the output circuit in lieu of an auxiliary winding 20 I provide a voltage divider at 8, connected in parallel with the primary 2a of the output transformer 2. The

monitoring voltage Em is derived from a portion of the voltage divider by a tap connection 9 leading to the primary 4a of the regulating transformer dflthrough blockingcondenser 5'. The circuit of the primary da is completed in the input of the amplifier through a separate source of input energy 3, the voltageof which, as indicated, is equal to the voltage of the main input source it connected in the grid circuit. The secondary 'lbof the regulating transformer 4 is connected with the source 3 and bias potential source 5 across the grid-cathode path of the tube l, as in Fig. l. v

The principal diiference, therefore, in the circuits of Figs. 1 and 2 is in the primary circuit of the regulating transformer 4, that in Fig. 1 including the same input source 3 as is connected in the grid circuit, with one side of the source connected with both primary and secondary wind Thus, the primary 4a. is energized by the voltages E1 and Em, and the secondary ib is responsive simultaneously to the differential of both voltages, through the transformer, and to the voltage E1 of the signal input directly from the source 3. In Fig. 2, the regulating transformer 4 has independent primary and secondary circuits, made possible by the provision of the separate in- The voltage E' between grid and cathode is the same as that in the circuit of Fig. 1, but the main input source 3 is relieved of such reaction as may be found in the source 3, Fig. 1, due to the effect of the currents in the primary la of the transformer d. In the circuit of Fig. 2, such reactions are confined to the separate source 3", and the operation of the amplifier is preserved subject to the signal input voltage, with the regulatory voltage simultaneously efiective, for delivering the amplified signal in proper form,

A unique feature of the regulator is that the turns ratio of the transformer 4 maybe increased indefinitely without causing oscillation in the system. It may be demonstrated mathematically that the A. C. plate resistance of the amplifier tube is reduced by a factor where a is the turns ratio of the regulator'transformer. For example, a class A audio amplifier employing a type 845 tube, with a regulator transformer having a turns ratio of 5:1, would have the following apparent characteristics:

Voltage gain, no 1oad=5 Apparent plate resistance:

jgg=3o0 ohms The amplifier stage, considered as a generator, has an internal impedance only one sixth of that of the unregulated amplifier.

It is seen that as the turnsratio of the transformer is increased, the apparent resistance of the amplifier tends toward zero. It should also be noted that it never becomes negative, which indicates that no oscillation can take place for high turns ratios. I

. I have disclosed my invention in certain preferred embodiments, but I desire it to be understood that further modifications may be made, and that I intendno limitations upon my inven tion except as' are imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. An electron tube amplifier comprising an electron tube having anode, grid and cathode electrodes; an anode circuit including output means and a source of power connected between said anode andsaid cathode; a grid circuit including a transformer secondary winding, input means, and a source of bias potential connected between said grid and said cathode; a transformer primary winding coupled with said secondary winding; and a series circuit including said primary winding, a direct current blocking condenser, means for deriving a voltage from. said output means, saidsources of power and bias potential, and means for derivinga voltage from said input means; said voltages derived from said input and said output means being connected in phase opposition under no load conditions in said output circuit, and said secondary winding being connected so that voltage thereacross is eiiective to counteract voltage variations in said output circuit under load conditions for substantially reducing said variations and the voltage in said secondary winding.

2. An electron tube amplifier comprising an electron tube having anode, grid and cathode electrodes; an anode circuit including output means and a source of power connected between said anode and said cathode, said output means comprising aprimary winding constituting an autotransformer having a tap connection there from connected with said source of power, and a secondary winding coupled with said primary winding for connection to a load; a regulating transformer having primary and secondary sec tions; a series circuit including said secondary section, input means, and a source of bias potential connected between said grid and said cathode;

and a series circuit including the primary section I of said regulating transformer, said input means, said sources of bias potential and power, said tap connection and a portion of the said primary winding separate from said anode circuit, and a blocking condenser; alternating voltages in the last said series circuit being connected in phase and a source of bias potential connected between said grid and said cathode; a transformer primary winding coupled with said secondary winding; and aseries circuit including said primary winding, a direct current blocking condenser, said tap connection and a portion of said voltage 'di vider, said sources of power and bias potential, and separate input means; alternating voltages in said series circuit being connected inphase opposition under no load conditions, and voltage in said secondary Winding under load conditions being effective to counteract voltage variations in said output means.

4. An electron tube amplifier as'set forth in claim 1, wherein said means for deriving a voltage from said output means comprises a portion of said output means separate fromsaid anode circuit, said source of power being connected to said output means by a tap connection to define the said portion.

5. An electron tube amplifier as set forth in claim 1, wherein said means for deriving a voltage from said output means comprises a voltage divider connected in parallel with said output means and a tap connection on said voltage divider connected with said primary winding through said blocking condenser.

6. An electron tube amplifier as set forth in claim 1, wherein said means for deriving a voltage from said input means comprises connections to said input means parallel to the connection thereof in said grid circuit.

7. An electron tube amplifier as set forth in claim 1 wherein said means for deriving a voltage from said input means comprises a separate device coupled with the input means and independent of the connection thereof in said grid circuit.

JOHN F. BYRNE. 

